The present invention is directed, in general, to an optoelectronic device and, more specifically, to an optoelectronic device having a barrier layer and an interface barrier layer located therein, and a method of manufacture thereof.
Optical fibers are key components in modern telecommunications and have gained wide acceptance. As is well known, telecommunication optical fibers are thin strands of glass capable of transmitting an optical signal containing a large amount of information over long distances with very low loss. Single fibers can carry multiple packets of data that are multiplexed on the fiber either by time division, where different slots of time are allocated to different packets, or by wave division multiplexing, where different wavelengths are allocated for different data. Optoelectronic devices, such as modulators and switches, perform the important function of adding information content to optical signals in optical communications systems. Such devices may include epitaxially grown multi quantum well type structures of an indium phosphide or indium gallium arsenic phosphide (InGaAsP) base. The quantum well type structures may be undoped, or may be doped with various n-type and p-type dopants.
The precision placement of the p-n junction in the active regions of optoelectronic devices is critically important for meeting the increasingly stringent requirements on device performance, such as modulation bandwidth, output power, extinction ratio, and uncooled operation. Zinc is presently the most commonly used p-type dopant in cladding and contact layers of various optoelectronic devices. These zinc layers are typically, but not necessarily, grown last, after active regions and blocking structures of the optoelectronic device have already been formed. Due to the high temperatures used to epitaxially grow layers by metalorganic vapor phase epitaxy (MOVPE), large amounts of zinc currently diffuse into the active region of the device. This zinc diffusion is highly undesirable because it can cause a shift of emitting wavelengths (up to tenths of microns) and reshaping of the zinc distribution profile. Moreover, the excess zinc in the active region may result in degradation of device characteristics, such as extinction ratio and junction capacitance in electroabsorbtion modulator structures.
One way the optoelectronic device manufacturing industry has attempted to substantially reduce the zinc diffusion into the active region, is to epitaxially form an undoped zinc set-back above the active region, prior to forming the zinc doped upper layer. The undoped zinc set-back, if manufactured correctly, is capable of substantially reducing the zinc diffusion into the active area. However, a problem with the zinc set-back layer, is that its optimal thickness is sensitive to the structure parameters (such as doping level and thickness) and growth conditions (growth rate and temperature) of the zinc-doped and contact layers. Thus, the zinc set-back layer needs to be customized for each device structure and reactor, which is time consuming and costly. Furthermore, the zinc set-back layer does not provide an adequate control, i.e., not reproducible, over the shape of the final zinc distribution in the upper layer.
Another way the optoelectronic device manufacturing industry has attempted to substantially reduce the zinc diffusion problems, is to incorporate a highly silicon doped layer between the zinc doped upper layer and the active region. This method tends to prevent the zinc from diffusing into the active region; however, the effectiveness of the silicon doping layer is very sensitive to the silicon doping level and the layer thickness. In addition, silicon is an n-type dopant, and when included between the upper layer and the active device, may form an additional, unwanted, p-n junction above the active region. This is generally undesirable as well, because it may degrade the device""s optical characteristics.
Accordingly, what is needed in the art is an optoelectronic device that does not encounter the problems associated with the prior art optoelectronic devices, and more specifically, an optoelectronic device, and a method of manufacture therefor, that prevents the diffusion of dopants into the active device regions.
To address the above-discussed deficiencies of the prior art, the present invention provides an optoelectronic device with superior quality. The optoelectronic device includes an active region located over a substrate, and an interface barrier layer and barrier layer located over the active region. The optoelectronic device further includes an upper cladding layer located over the interface barrier layer and the barrier layer. In an exemplary embodiment of the invention, the interface barrier layer is an indium phosphide interface barrier layer and the barrier layer is an indium gallium arsenide phosphide barrier layer.
Thus, one aspect of the present invention provides an optoelectronic device that does not experience substantial dopant diffusion into the active region, as experienced in the prior art optoelectronic devices. Moreover, the present optoelectronic device does not experience the higher threshold current, lower slope efficiency, and leakage of current out of the active region, as experienced in the prior art optoelectronic devices.
An alternative aspect of the invention provides a method of manufacturing the previously mentioned optoelectronic device. The method includes (1) forming an active region over a substrate, (2) forming an interface barrier layer over the active region, (3) forming a barrier layer over the active region, and (4) forming an upper cladding layer over the interface barrier layer and the barrier layer. Also included in the present invention, is an optical fiber communications system. The optical fiber communication system, in an advantageous embodiment, includes an optical fiber, a transmitter and a receiver connected by the optical fiber, and the optoelectronic device illustrated above.